Method for fractionation of vegetable proteins by reduction

Abstract

A method for fraction fractionation of a vegetable protein such as soybean protein which comprises subjecting a source of the vegetable protein in an aqueous system to reduction conditions such as treatment with a sulfite compound, a glutathione compound or cysteine compound, or electrolytic reduction at pH within a neutral or alkaline range and then bringing the system to pH of 5.5 to 7.0 at a temperature of 20 DEG C. or lower to fractionate the system into a soluble or dispersing fraction and an insoluble or precipitate fraction.

What is claimed is: 
     
       1. A method for fractionation of a vegetable protein which comprises dispersing a source of the vegetable protein containing insoluble carbohydrate in an aqueous system at pH of 7.1 to 9 under reduction conditions with (a) at least 0.5% by weight of a sulfite compound based on the source,   (b) at least 5 m moles of a glutathione compound per 100 g of the source, or   (c) at least 5 m moles of a cysteine compound per 100 g of the source without the addition of sodium chloride and then bringing the resulting mixture to pH 5.5 to 7.0 at a temperature of 20° C. or lower to fractionate the mixture into a soluble or dispersing fraction and an insoluble or precipitate fraction accompanied by the insoluble carbohydrates.     
     
     
       2. A method according to claim 1, wherein the vegetable protein is soybean protein. 
     
     
       3. A method according to claim 1, wherein the sulfite compound is selected from a group consisting of sulfurous acid, alkali metal sulfites, ammonium sulfite, alkali metal bisulfites, ammonium bisulfite, alkali metal pyrosulfites, ammonium pyrosulfite, alkali metal metabisulfites, ammonium metabisulfite and sulfur dioxide. 
     
     
       4. A method according to claim 1, wherein a glutathione compound or a cysteine compound is selected from the group consisting of glutathione, glutathione hydrochloride, cysteine and cysteine hydrochloride. 
     
     
       5. A method according to claim 1, wherein the method further comprises isolating the insoluble fraction, and dispersing it in warm water to remove a precipitate. 
     
     
       6. A method according to claim 1, wherein the method further comprises isolating the soluble fraction, subjecting it to isoelectric precipitation, separating a precipitate, neutralizing it, heating and then drying it. 
     
     
       7. A method for fractionation of a vegetable protein composed of 7S and 11S protein fractions which comprises subjecting a source of the vegetable protein containing insoluble carbohydrate in an aqueous system to electrolytic reduction and then bringing the system to pH 5.5 to 7.0 and the temperature to 20° C. or lower to fractionate the system into a soluble or dispersing fraction and an insoluble or precipitate fraction. 
     
     
       8. A method according to claim 7, wherein the vegetable protein is soybean protein. 
     
     
       9. A method according to claim 7, wherein the electrolytic reduction is carried out in the presence of a sulfite compound, a sulfate compound, a glutathione compound or a cysteine compound. 
     
     
       10. A method according to claim 9, wherein the sulfite compound is selected from a group consisting of sulfurous acid, alkali metal sulfites, ammonium sulfite, alkali metal bisulfites, ammonium bisulfite, alkali metal pyrosulfites, ammonium pyrosulfite, alkali metal metabisulfites, ammonium metabisulfite and sulfur dioxide. 
     
     
       11. A method according to claim 9, wherein the sulfate compound, the glutathione compound or the cysteine compound is selected from the group consisting of sodium sulfate, glutathione, glutathione hydrochloride, cysteine and cysteine hydrochloride.